Three-dimensional Streamlines Research Articles

Chebyshev spectral Newton iterative analysis on unsteady oblique stagnation flow of Maxwell fluids over an oscillating-rotating disk with Cattaneo–Christov double diffusion

Oblique stagnation flow on a rotating disk is commonly observed in processes such as spinning coating and thin film deposition techniques. The investigation of the unsteady oblique stagnation point flow for Maxwell fluid over an oscillating-rotating disk embedded in a porous medium is meticulously conducted by employing the Darcy–Maxwell framework in conjunction with Cattaneo–Christov double diffusion model. A transformation of similarity is applied to reframe the governing equations into a system of non-dimensional coupled partial differential equations, whose numerical solutions are secured by the Chebyshev Spectral Newton Iterative Scheme. The outcomes underscore that an escalation in the Darcy parameter escalates the resistance within the porous medium, consequently leading to a reduction in velocity. Both the first-order slip and the second-order slip mitigate the fluid's interaction with the disk wall, leading to a retardation in flow velocity. Additionally, the presence of augmented thermal radiation parameters is observed to enhance heat transfer efficiency, resulting in a more homogenized temperature distribution. The two-dimensional and three-dimensional streamlines provide a precise depiction of the flow characteristics at the oblique stagnation point on the oscillating-rotating disk. These findings offer a theoretical foundation that can be instrumental for forthcoming research in analogous fields.

Flow characteristics and heat transfer performance in tubes with dimples-protrusions

Dimple and protrusion are microstructures processed on the surface of heat transfer tubes to improve thermal-hydraulic performance (THP). However, the effect and mechanism of composite structures composed of dimples and protrusions (dimples-protrusions) on the THP are still unclear. In this work, heat transfer tubes with simple dimples (DT-SC) and different cross-section dimples-protrusions (DT-RRRS, DT-RCRS, and DT-RTRS) are chosen to explore the impact of dimples-protrusions on THP compared to dimples. Various parameters, such as velocity, three-dimensional streamline, pressure, etc., are used to reveal the mechanism of the influence of dimples-protrusions on THP. The research presents that dimples-protrusions can improve the intensity of the fluid impinges on the wall and expand the area of secondary flow compared to dimples, resulting in a significant increase in THP. The PEC of DT-RRRS is increased by 7.9 % compared with that of DT-RS at Re = 5000. In addition, the dimples-protrusions with different cross-sections have different effects on THP due to differences in the distribution of secondary flow and the impingement of fluid on the wall. The impact of dimples-protrusions depth on THP is closely related to Re. DT-RCRS can achieve a maximum PEC of 1.38 under the conditions of Re = 5,000, H1 = 2 mm, and H2 = 1 mm. This work provides a reference for the design of dimples-protrusions to achieve optimal THP.

Large Eddy Simulation of Pulsed Film Cooling with a Dielectric Barrier Discharge Plasma Actuator

The effects of the coolant pulsation and the plasma aerodynamic actuation (PAA) on the film cooling are herein explored via large eddy simulations. The electrohydrodynamic force derived from the PAA was solved through the phenomenological plasma model. The Strouhal number of the sinusoidal coolant pulsation and the averaged pulsation blowing ratio were 0.25 and 1.0, respectively. Comprehensive analyses were carried out on the time-averaged flow fields, and the results reveal that the pulsed cooling jet might cause a deeper penetration into the crossflow, and this phenomenon could be remarkably mitigated by the downward force of the PAA. Comparing steady film cooling to pulsed film cooling revealed a modest 15.1% reduction in efficiency, while the application of the dielectric barrier discharge plasma actuator (DBDPA) substantially enhanced the pulsed film cooling efficiency by 42.1%. Moreover, the counter-rotating vortex pair (CRVP) was enlarged and lifted off from the wall more poorly due to the coolant pulsation, and the PAA weakened the detrimental lift-off effect and entrainment of the CRVP. Then, the spatial–temporal development of the coherent structures was figured out by the alterations in the centerline temperature, reflecting the formation of the intermittent coherent structures rather than hairpin vortices due to the coolant pulsation, and their size and upcast behaviors were reduced by the PAA; thus, the turbulent integration of the coolant with the crossflow was suppressed fundamentally. Finally, the three-dimensional streamlines confirmed that the coherent structure dynamic behaviors were significantly regulated by the PAA for alleviating the adverse influences of the coolant pulsation. In summary, the PAA can effectively improve the pulsed film cooling efficiency by controlling the spatial–temporal development of the dominant coherent structures.

Flow control mechanism of compressor cascade: A new leading-edge tubercles profiling method based on sine and attenuation function

Leading-edge tubercles are an effective method to improve the stall margin in a compressor. In existing studies on leading-edge tubercles, achieving a better control on all conditions is a huge difficulty and challenge. Hence, a new method of leading-edge tubercles profiling based on sine and attenuation functions is introduced in this paper. First, the wavelength and amplitude of the leading-edge tubercles were varied by sine function to study their effects on compressor performance. The research reveals uniform tubercles with small amplitude and large wavelength can delay stall incidence from 7.9° to 8.8° and increase it by 10% compared to the baseline. A small amplitude is beneficial to reduce the additional loss caused by the leading-edge tubercles near the blade middle, and a large wavelength is conducive to the development of separation vortex. Then, the leading-edge tubercles were further modified and investigated by introducing some attenuation functions. A suitable attenuation function is introduced to the uniform tubercles with small amplitude and large wavelength so that stall incidence is delayed to 9.7° and increased by 21.25% compared with the baseline. Finally, the vorticity transport equation and three-dimensional streamline reveal that the formation and development of leading-edge vortex pairs are mainly related to the axial bending of the circumferential vortex, the axial stretching of the axial vortex, and vortex viscous dissipation. For this paper, the principal purpose is to offer useful design guidelines, study flow control mechanisms, and achieve better aerodynamic performances under all working conditions for the leading-edge tubercles in the compressor.

A Method of Urban Wind Field Visualization Based on Deep Learning

In order to solve the problems of incomplete feature extraction, visual results that disrupt the continuity of the flow field, and unstable clustering resulting in poor streamline representation during urban wind field visualization, a three-dimensional streamline visualization method based on deep learning was proposed. This method consists of two parts: one is streamline feature learning, and the other is clustering method. The Euclidean distance represented by the streamline is used as the similarity between the streamlines for clustering, and the clustering results obtained are weighted and combined before being divided. The method was tested on a real urban wind field dataset and qualitatively compared with existing methods. The results show that this method can better balance the relationship between feature extraction and streamline distribution compared to existing methods.

Engineering performance and microscale structure of activated high titanium slag-soil-cement-bentonite (HTS-SCB) slurry backfill

An innovative soil-cement-bentonite (SCB) slurry composed of cement, clay soil, bentonite and reactive high titanium slag (HTS) was synthesized to block the migration of contaminants in groundwater at tailings ponds. Mechanical activation was applied to activate the HTS, and partial cement was replaced by the reactive HTS. The engineering performance indices of the HTS-SCB slurry, such as the slump, hydraulic conductivity, compressive strength, porosity and leaching risks of heavy metals, were evaluated in this study. The hydration products were identified through a series of analytical tests. The three-dimensional microscale structure of the sample was obtained from the CT experiment, and the microscale geometrical properties were analysed using pore-network models and Avizo software. The lattice Boltzmann method (LBM) was applied to simulate the fluid flow in the HTS-SCB slurry, and the simulated hydraulic conductivities and three-dimensional streamlines were obtained. The results showed that the HTS-SCB slurry had an optimal anti-seepage performance, appropriate mechanical performance and low leaching risks of heavy metals when the cement was replaced by 50 % reactive HTS. The hydration reaction between calcium hydroxide and HTS generates large amounts of fresh calcium silicate hydrates containing Fe and Ti, which fill the pores and contribute to low hydraulic conductivity, micropores (diameter ≤ 2.8 μm) and microflow paths (diameter ≤ 2.5 μm). The LBM results show that the calculated hydraulic conductivities match well with the measured values, and a high tortuosity is obtained from the three-dimensional velocity fields. The HTS-SCB slurry can satisfy the requirement of cut-off walls in land remediation applications and realize solid waste recycling, energy conservation and emission reduction and sustainable development.

Assessment of new pressure-corrected design method for hypersonic internal waverider intake

The osculating axisymmetric flows concept is an extension of the concept of the osculating cones for designing waveriders which is also utilized to design the three-dimensional internal waverider intake, where the three-dimensional flowfield is generated using slices of locally two-dimensional flow. However, this design methodology neglects the effect of cross-flow between the osculating planes, which causes lateral pressure gradients. Therefore, this article introduces and assesses a new pressure-corrected osculating axisymmetric flows design approach for the three-dimensional internal waverider intake. The new design concept adds the lateral pressure gradient correction into the original design concept using cross-flow velocities calculated by Euler’s incompressible flow equation between the osculating planes. Thereafter, three-dimensional streamlines are formed instead of the osculating plane’s two-dimensional streamlines. The new design procedure is presented in detail and then verified using wavecatcher intake with a circular shape that contains zero lateral pressure gradients. No geometry changes are found when the pressure-corrected wavecatcher intake is compared with the uncorrected wavecatcher intake. Moreover, four hypersonic wavecatcher intakes of semi-rectangular and rectangular entrance and exit shapes are designed with a design point of Mach number 6.0 and numerically studied to assess the new design approach. The results revealed that the pressure-corrected wavecatcher intakes exhibited better total pressure recovery, flow uniformity, Mach number, and kinetic energy efficiency than uncorrected wavecatcher intakes. While the impinged shockwave is attached to the intake’s entrance, and the mass flow is completely captured in all designs. It is found that 38.49% and 30.36% of the exit area of the pressure-corrected wavecatcher intakes, and 35.68% and 28.37% of the exit area of the uncorrected wavecatcher intakes, have provided the combustor with air having a total pressure recovery above 0.7, respectively.

Numerical Simulation Analysis on Hydraulic Optimization of the Integrated Pump Gate

Based on the Reynolds time mean N-S equation and standard k-ε turbulence model and using Computational Fluid Dynamics technology, this study aims to integrate the brake pump to carry out numerical simulation. Through the adoption of different arrangements of impending height and spacing, the hydraulic characteristics of the full tubular pump unit are analyzed. The two-dimensional streamline, velocity and pressure distribution, and three-dimensional streamline, axial velocity and vorticity distribution of the front pool of each scheme are displayed. The results show that the recommended pump installation height is 0.8 Dd, the maximum limit value of the pump station design specification; in the dual-pump mode, the recommended pump spacing is 2.00 Ds.

Validation of time-resolved, automated peak trans-mitral velocity tracking: Two center four-dimensional flow cardiovascular magnetic resonance study

ObjectiveWe aim to validate four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) peak velocity tracking methods for measuring the peak velocity of mitral inflow against Doppler echocardiography. MethodFifty patients were recruited who had 4D flow CMR and Doppler Echocardiography. After transvalvular flow segmentation using established valve tracking methods, peak velocity was automatically derived using three-dimensional streamlines of transvalvular flow. In addition, a static-planar method was used at the tip of mitral valve to mimic Doppler technique. ResultsPeak E-wave mitral inflow velocity was comparable between TTE and the novel 4D flow automated dynamic method (0.9 ± 0.5 vs 0.94 ± 0.6 m/s; p = 0.29) however there was a statistically significant difference when compared with the static planar method (0.85 ± 0.5 m/s; p = 0.01). Median A-wave peak velocity was also comparable across TTE and the automated dynamic streamline (0.77 ± 0.4 vs 0.76 ± 0.4 m/s; p = 0.77). A significant difference was seen with the static planar method (0.68 ± 0.5 m/s; p = 0.04). E/A ratio was comparable between TTE and both the automated dynamic and static planar method (1.1 ± 0.7 vs 1.15 ± 0.5 m/s; p = 0.74 and 1.15 ± 0.5 m/s; p = 0.5 respectively). Both novel 4D flow methods showed good correlation with TTE for E-wave (dynamic method; r = 0.70; P < 0.001 and static-planar method; r = 0.67; P < 0.001) and A-wave velocity measurements (dynamic method; r = 0.83; P < 0.001 and static method; r = 0.71; P < 0.001). The automated dynamic method demonstrated excellent intra/inter-observer reproducibility for all parameters. ConclusionAutomated dynamic peak velocity tracing method using 4D flow CMR is comparable to Doppler echocardiography for mitral inflow assessment and has excellent reproducibility for clinical use.

Numerical study on adjustment of the main flow field with guide vanes in transition zone for an S-duct

A 30°/30° S-duct is often employed by a modern civil and military aircraft. Due to the vortex generators have poor control effect on the flow separation in the large curvature S-duct, so a new method adjusting the direction of the main flow in the transition zone for S-duct is proposed in the present study. These studies are carried out by solving Navier-Stokes equations with SST k-ω turbulence model. In order to explore the control mechanism of guide vanes on the flow field for S-duct, the internal flow field of S-duct with/without guide vanes is analyzed and compared in detail, including the velocity distribution on the symmetry plane, the secondary vortex intensity at different cross sections, turbulent kinetic energy on different cross sections, total pressure distribution on different cross sections, three-dimensional streamline, and so on. The results show that guide vanes can not only effectively adjust the direction of the main flow, but also restrain the flow separation, reduce the total pressure loss, and improve the uniformity of flow field.

Bödewadt flow of Bingham fluid over a permeable disk with variable fluid properties: A numerical study

This study is primarily motivated to explore the onset of fluid yield stress on the Bödewadt flow involving Bingham fluid whose viscosity coefficient admits an inversely linear temperature dependency. Accompanying heat transfer process is studied by assuming isothermal surface temperature. A similarity solution is presumed which results into a system of coupled non-linear equations with three unknowns. Numerical solutions reveal that ignoring viscosity variation with temperature can lead to inaccurate calculations of skin friction coefficient and Nusselt number, which are important quantities from engineering viewpoint. For pure Bödewadt flow, axial flow accelerates and radial flow reduces when case of constant fluid properties is approached. In addition, a considerable growth in cooling rate of the surface is detected whenever suction velocity becomes higher. Both two-and three-dimensional streamlines are computed which reveal that Bingham fluid assumption combined with variable viscosity markedly affects the flow situation.

In-situ X-ray tomography on permeability evolution of C/SiC porous ceramic for hypersonic vehicles

Transpiration cooling system in hypersonic vehicles still remains a challenge due to the limitations of observing permeability and microstructure evolution of porous medium filled with coolant. To tackle this problem, a novel compression-permeation device is designed with high-resolution X-ray tomography system, and then an investigation on permeability evolution mechanism of a C/SiC porous ceramic under pressure is performed using in-situ X-ray imaging and the compression-permeation device. The experimental results indicate that the pore-space fluid flow is displayed in terms of three-dimensional streamlines, making the permeability mechanism clear. Meanwhile the porosity along the thickness of ceramic under pressure has been obtained by synchrotron tomography testing, and it is also verified that the porosity of C/SiC ceramic fabricated in our research group is basically uniform (>95.4%) along the thickness. Furthermore, we have found the evolution rule for permeability of porous ceramic with water, which depends on the variation of its microstructure under different loads.

Prediction for future occurrence of type A aortic dissection using computational fluid dynamics.

The actual underlying mechanisms of acute type A aortic dissection (AAAD) are not well understood. The present study aimed to elucidate the mechanism of AAAD using computational fluid dynamics (CFD) analysis. We performed CFD analysis using patient-specific computed tomography imaging in 3 healthy control cases and 3 patients with AAAD. From computed tomography images, we made a healthy control model or pre-dissection model for CFD analysis. Pulsatile cardiac flow during one cardiac cycle was simulated, and a three-dimensional flow streamline was visualized to evaluate flow velocity, wall shear stress and oscillatory shear index (OSI). In healthy controls, the transvalvular aortic flow was parallel to the ascending aorta. There was no spotty high OSI area at the ascending aorta. In pre-dissection patients, accelerated transvalvular aortic flow was towards the posterolateral ascending aorta. The vortex flow was observed on the side of the lesser curvature in mid-systole and expanded throughout the entire ascending aorta during diastole. Systolic wall shear stress was high due to the accelerated aortic blood flow on the side of the greater curvature of the ascending aorta. On the side of the lesser curvature, high OSI areas were observed around the vortex flow. In all pre-dissection cases, a spotty high OSI area was in close proximity to the actual primary entry site of the future AAAD. The pre-onset high OSI area with vortex flow is closely associated with the future primary entry site. Therefore, we can elucidate the mechanism of AAAD with CFD analysis.

Infill well placement optimization in two-dimensional heterogeneous reservoirs under waterflooding using upscaling wavelet transform

Optimal location of infill wells is very important in the development strategies of any reservoir. It is even one of the most challenging tasks for waterflooding projects in heterogeneous reservoirs. The new infill wells have to be located based on optimum reservoir management practice taking into considerations several reservoir parameters. Usually, there are several potential locations of the new infill wells. Selecting and evaluating of all the possible candidate wells using fine scale models is neither computationally straightforward nor time efficient for geological models consisting of millions of grid cells. This paper presents a practical and cost effective method that minimizes the number of simulation runs and maximizes oil recovery by optimizing infill well location. The proposed method consists of upscaling the geological reservoir model from fine scale into a coarser scale while preserving the important characteristics of the fine scale model. The proposed approach uses wavelet transform as an upscaling technique. To illustrate its feasibility and effectiveness, the proposed method is applied to three synthetic cases of two-dimensional inverted five-spot heterogeneous reservoir models. Static Dykstra-Parsons coefficient of permeability variation is utilized to compute the degree of heterogeneity of each of the three models. Permeability distribution values are used to represent and construct the reservoir models. The permeability models are upscaled from the original fine grid model to coarser scale levels. A computationally efficient and extremely time saving three-dimensional streamline simulator is used to implement the proposed approach. This paper shows that the results obtained from the upscaled models are in excellent agreement with the fine scale models. More importantly, the results also illustrate that the proposed method extensively reduces the number of simulation runs required to find the optimum well location between 75% and 93% depending on the reservoir heterogeneity. The methodology presented in this paper provides a straightforward road map for upscaling several heterogeneous reservoir models using wavelet transform approach to determine the optimum infill well location.

Three-Dimensional Streamline Tracing Method over Tetrahedral Domains

Getting a clear understanding of the fluid velocity field in underground porous media is critical to various engineering applications, such as oil/gas reservoirs, CO2 sequestration, groundwater, etc. As an effective visualization tool and efficient transport behaviors solution algorithm, the streamline-based method was improved significantly by numerous studies conducted in the last couple of decades. However, the implementation of streamline simulation is still challenging while working with Finite Element Method (FEM) over 3D tetrahedral domains, where the mass conservation is not guaranteed. Considering the increased computational cost to enforce mass conservation in FEM and additional complexity, a new three-dimensional streamline tracing algorithm is presented that only relies on the velocity vector of a flow field on each vertex of a tetrahedron in a 3D unstructured mesh system. Owning to the shape functions and transformation equations between the master element and actual element, the exit coordinate leaving a tetrahedral element can be determined effectively. As a result, Time of Flight (TOF), the coordinate variable along each streamline, can be calculated accurately and efficiently because that the analytical solution depicting the trajectory in Master Element is deduced. The presented streamline-based method is tested under FEniCS, a programming framework for FEM, which eases the implementation and further development of the presented method.

Oblique stagnation flow towards a rotating disc

This work endeavours to study the problem of axisymmetric oblique stagnation point flow above a rotating disc. An external flow impinges obliquely on a disc when the disc is rotating with constant angular velocity. Suitable similarity variables are introduced, for the first time, to transform the governing Navier–Stokes equations into a highly nonlinear system of ordinary differential equations, governed by a rotation ratio parameter α and an obliquity parameter γ. These resulting equations are then solved numerically via the routine bvp4c function from MATLAB software. Impact of different parameters on the flow and velocity profiles are discussed through tables and graphs. Further, three-dimensional streamlines are drawn to reveal the detailed effects of the parameters on the flow domain. It is noticed that streamlines are to shift the location of the stagnation point towards the incoming flow. There is also a rotational motion around the stagnation point for the rotating disc case.

On the spreading of non-canonical thermals from direct numerical simulations

We present results from direct numerical simulations on laminar and turbulent non-canonical thermals with an initial rectangular density distribution at a Reynolds number of Re = 500 and Re = 5000, respectively. We find the non-canonical shape to induce strong azimuthal variations in the thermal for both the laminar and turbulent cases. These include noticeable differences in downward and horizontal propagation speeds as well as differences in the strength of the vortex tube. These differences persist over a significant period of time and help generate a cross-flow component that is otherwise not present in canonical cases. The cross-flow component is in the opposite direction to that observed in gravity currents with the same initial density distribution. This is counterintuitive seeing that both flows are solely driven by buoyancy. By extracting the three-dimensional streamlines, we find the descending vortex tube to force the dense fluid to follow a helical path.

Analysis of Seepage Characteristics of Complex Pore Structure Rock by Digital Core Method

Application of traditional rock physics experimental methods in investigating the macroscopic pertrophysical properties of low porosity, low permeability, and high complexity pore structure reservoirs is limited by the high cost, long cycle, large error, and specific difficulties of such reservoirs. It is also difficult to evaluate quantitatively the influence of microscopic reservoir structure on rock physical properties. Application of micro-CT scanning and advanced imaging processing technology enables one to establish an accurate representative pore space model equivalent to the true core structure. Numerical simulation with Avizo-XLab solver method was used to calculate the pore fluid flow based on the Navier-Stokes equation and the Darcy seepage law. The visualization method helped to display the pore-space fluid flow in a three-dimensional streamline, and the pore pressure distribution field is displayed, making the simulation results clear and intuitive. Research shows that numerical simulation based on the digital platform provides an instrument for the measurement of the fluid micro flow and the rock seepage parameters. This paper provides a new method for digital research on rock physical properties which helps to overcome the deficiency of traditional rock physics experimental research.

Numerical analysis of the groove effect on the tip leakage vortex cavitating flow

In this paper, the groove effect on the tip leakage vortex cavitating flow characteristics of a simplified NACA0009 hydrofoil with tip gap is studied. Considering local rotation characteristics and curvature effects of the tip leakage vortex flow, the rotation-curvature corrected shear-stress-transport turbulence model is applied to simulate the time-averaged turbulent flow. The Zwart–Gerber–Belamri cavitation model is used to simulate the cavitating flow. The results show that the groove could affect the tip leakage vortex cavitating flow. The groove enhances the interaction between the tip leakage flow and main flow, and then it affects the cavitation of the tip leakage vortex. Compared with the non-groove case, for groove cases of αgre ≤75°, the tip leakage vortex cavitating flow is suppressed, the flow pattern in the gap is improved, and the mean leakage velocity Vlk &lt; 0.8. The region of high leakage velocity is eliminated and the distribution of the pressure is more uniform. The tip leakage vortex cavitation area is reduced, and the maximum decrease is 72.90%. While for groove cases of αgre≥90°, neither the tip leakage vortex cavitating flow nor flow pattern in the tip gap is ameliorated, the mean leakage velocity Vlk lies the range from 0.90 to 0.96. The region of high leakage velocity still exists and even the tip leakage vortex cavitation area is increased. Based on three-dimensional streamlines and vorticity transport equation, the interaction between the tip leakage flow and main flow leads to the variation of the tip leakage vortex cavitating flow. This paper aims for a useful reference to mitigate the tip leakage vortex cavitation and control the influence of the tip leakage vortex cavitating flow for the hydraulic machinery.

A GPU-based multi-level algorithm for boundary value problems

A novel geometric single-grid multi-level (GSGML) algorithm is presented for the numerical solution of boundary value problems (BVPs). The algorithm is specifically designed for parallel scalability with high occupancy of streaming processors inside many-core architectures like the Graphics Processing Unit (GPU). The algorithm consists of iterative, superposed operations on a single grid, and is composed of two full-grid routines: a restriction and a coarsened interpolation–relaxation. The restriction is a local average of scalar or vector fields, and the interpolation–relaxation is a simultaneous application of coarsened finite-difference operators and interpolations in complementary subsets of the grid. The routines are scheduled in a saw-like refining cycle. Convergence to machine precision is achieved repeating the full cycle using residuals and superposition. The algorithm is attractive for its computational simplicity and provides a competitive GPU-based fast solver for elliptic partial differential equations like the Poisson–Helmholtz equation. Applications shown in this work include the deformation of two-dimensional grids, the computation of three-dimensional streamlines for a singular trifoil-knot vortex and the calculation of three-dimensional electric potentials in heterogeneous dielectric media.